1. Field of the Invention
Embodiments disclosed herein generally relate to the structure of a perpendicular magnetic write head for use in a magnetic disk drive.
2. Description of the Related Art
Over the past few years, shingled magnetic recording (SMR) has been studied as a recording technique for improving the areal density. FIG. 1 shows a diagram 100 of one example of the SMR technique. In this technique, multiple tracks 103 overlap and are written in a shingle pattern. A partial view of a magnetic recording head 105 is shown and the magnetic recording head 105 moves over the tracks 103 in the direction of the arrow 107, while progressive scans are in the direction of the arrow 111. Magnetic flux is applied to the magnetic recording head 105 in the direction of the arrow 109. With the SMR technique, an actual read track is written by using the end of the main pole, and thus, the write characteristics in the end of the main pole are important. Specifically, the magnetic field gradient in the cross-track direction and the magnetic field gradient in the down-track direction at the track edge must be improved.
Previously, for improving the write characteristics at the track edge, increasing the magnetic field gradient was attempted by reducing two side gaps 204 on either side of a main pole 202, as shown in FIG. 2. Comparing the first magnetic head 200 to the second magnetic head 201 in FIG. 2, magnetic head 200 has significantly wider side gaps 204 than magnetic head 201. However, by only narrowing the side gaps 204 in magnetic head 201, the problem of the absorption of the magnetic field into the side shields 208 and inadequate strength arose, and consequently, the inability to obtain the desired magnetic field gradient.
In addition, over the past few years, microwave-assisted magnetic recording (MAMR) has been studied as a technique for effectively improving the write magnetic field strength. In MAMR, the effective write magnetic field gradient can be increased by an alternating current (AC) magnetic field generated by a spin torque oscillator (STO). The STO is composed of a field generation layer (FGL) for generating the AC magnetic field, a spacer layer (spacer), and a spin polarization layer (SPL) for transmitting the spin polarized torque, and is typically placed in the center of the main pole on the trailing shield side of the main pole. By applying the magnetic field from the writer to the STO and conducting current to the STO, the STO oscillates, and the AC magnetic field is applied to the medium.
It is possible to combine the SMR and MAMR techniques. However, in a narrow track high-areal-density hard disk drive (HDD), the maximum MAMR assist effect must be implemented at the track edge in order to achieve a high signal-to-noise ratio (SNR), and the cross track gradient and down track gradient at the track edge must be increased. By only placing the STO in the center of the main pole on the trailing shield side of the main pole, the magnetic field gradient at the track edge could not be increased, and adequate gain could not be obtained by the MAMR-SMR technique.
FIGS. 3A-3B show a magnetic recording head 300 with an STO 306 having a conventional rectangular shape. FIG. 3A shows the magnetic head 300 viewed from the surface of a media facing surface (MFS) such as an air-bearing surface (ABS). The magnetic head 300 includes a trailing shield 312. FIG. 3B shows a cross-sectional at the contact surface between the main pole 302 and the STO 306 of the recording head 300. With this recording head 300, the side gap 304, which is located next to the STO 306, has been reduced in size while the side gap 314 has not. However, the narrower side gap 304 must be widened to insulate the side shield 308 and the STO 306. This results in the degradation of the cross track gradient of the write magnetic field. As a result of the degradation of the AC magnetic field gradient strength in magnetic head 300, the SNR does not improve because the conduction region 416 to the STO 306 has decreased, as shown in FIG. 4.
Therefore, there is a need in the art for a perpendicular magnetic write head having improved SNR.